Watermarking pellicle



Patented July 6, 1937 UNITED" srArss 2,086,178 WATERMARKING PELLICLEJames E. Snyder, Kenmore, N. Y., assignor, by

mesn'e assignments, to E. I. 'du Pont de Nemours & Company, Wilmington,Del., a corporation of Delaware No Drawing. Application January 15,1934, Serial No. 706,710

Claims. (01. 1848)' This invention relates toa new article ofmanufacture. The invention relates to a process of manufacturing the newarticle. More particu- 5 larly the invention relates to a process ofmanufacturing a watermarked pellicle of non-fibrous cellulosiccharacter. Still more particularly the invention relates to themanufacture of watermarked regenerated cellulose pellicles.

The watermarking of paper is an old and wellknown process by which asheet of paper carries a mark, design, or picture substantiallyinvisible by reflected light but visible by transmitted light. Thewatermarking process has enabled paper 15 manufacturers to identifytheir products and to prevent the deception of the public.

There is on the market a non-fibrous, non-porous, transparent tissue,ordinarily used for wrapping purposes, comprising regenerated cellulosefilm. Other sheets of similar non-fibrous character have been made fromcellulose esters such as cellulose acetate, and from cellulose ethers.No satisfactory method has been developed for imparting to these sheetsa mark similar in character to a watermark such as is used in paper.Attempts have been made to impress a mark upon the finished sheet bymoistening and die-pressing but the results have been unsatisfactory forvarious reasons, for example, the mark lacks suitable permanence.Attempts to mark the sheeting in manufacture after it has been at leastpartially coagulated but before it has been completely regenerated havenot been entirely successful because the pellicle shrinks greatly duringdrying and the impression is distorted and in some cases disappears.

One object of this invention pertains to the production of a dense,smooth, non-porous, nonfibrous, preferably transparent cellulose filmhaving imparted thereto permanent indicia, such as numbers, letters andthe like. Another object of the invention pertains to the production offilms of this character, comprising regenerated cellulose. A furtherobject of the inventioncomprises production of film of the characterdescribed carrying indicia similar in appearance and character to thewatermarking used in paper.

Other objects of the invention will appear hereinafter.

,. The invention will be described most particularly in its applicationto the manufacture of regenerated cellulose pellicles. It is to beunderstood that this description is illustrative and not limitative.

, In the manufacture of regenerated cellulose sheeting by one method, aviscous solution is forced through a thin, elongated orifice ofuniformWidth into and beneath the surface ofa coagulating bath wherein theviscous is" precipitated and the. regeneration commenced and somee timescompleted. The pellicle thusfornied is passed through additionalregenerating, washing, desulfuring, and glycerinating baths, andoccasionally through other baths designed to accomplish particular ends,and from these baths is passed to the driers. In the ordinary pellicle.manufacturing machine the drier consists 'of a series of heated rollersover the surfaces of which the pellicle travels, being wound up at theend. in a dried and completely usable condition. I

It is my discovery that if the pellicle beimf-f pressed whenit ispartially dried, for instance, by impression with a die having raisedfigures-or designs, it will retain the impressionperm'anently. It isdesirable that the impression bemade at a particular stage in thedrying. The impres 207 r siori, for all practical purposes, ,must' bemade upon the pelliclewhen the moisture content of the pellicle has beenreduced to between about 45% and about,190% of the weight of the drypellicle plus glycerine (or other softener). Preferably, the impressionshould be made at 2. moisture content of about 100% because better andmore uniform results are obtained. However, it is possible to obtainadvantages'of the invention occasionally at moisture percentages of 4.5%and even lower and moisture percentages of 190% or even higher. When theimpressions are. made with m.oderate pressure at a moisture content lessthan about 45%, the impressions are so faint as to be either invisibleor scarcely discernible. Impressions made at moisture contents abovevabout 190% become distorted during drying and unless the pressures usedare veryhighgradually .1 fade out, being substantially unrecognizable orentirely invisible at the completionfof theman'u 10 facturing operation.I f

It should be understood thatit is not desirable to use heavy pressuresto impress the pellicle because heavy pressures'tenid to puncture or torupture; the pellicle. In ordinary practice, a die roller, bearing onits surface 'a raised insignia or design, will be placed in contact witha dryer roller. The pellicle will be passed between the impressingroller and the dryer roller and will receive the impression from thedie. It is necessary that the pressure exerted by the die against thepellicle be sufiicient to impart to the pellicle a permanent mark. Theactual pressure usedv for impressing a pellicle can readily bedeterminedby experiment. The magnitude i of the pressure will depend somewhat onthe size and design of the dies, the number of impressions imparted tothe pellicle in a unit of area, and upon the material of Which the dieis made. Similarly, the pressure used will vary, depending upon the typeof pellicle which is being manufactured. The Watermark can be given anembossed appearance by impressing the sheet With a die against aroughened surface. For example, a satisfactorily embossed appearance canbe obtained by covering the dryer roll, with which the roller carryingthe die contacts, with a fine mesh screen. The embossed Watermark can beseen by reflected as well as by transmitted light. An embossed surfacecan also be obtained by impressing against a smooth roller with a diehaving an embossed or roughened surface. If both the die and thesupporting surface are smooth, the watermark is visible by reflectedlight at certain angles only.

This invention may be applied to the marking of tubes, caps, bands, andother pellicles of regenerated cellulose in the same manner as has beendescribed for sheets of regenerated cellulose.

The invention is applicable to the manufacture of cellulose ester andcellulose ether pellicles obtained from aqueous solution. In themanufacture of cellulose acetate, for example, cellulose acetatedissolved in a suitable aqueous solution may be cast into an aqueouscoagulating bath. The film is then passed through suitable washing tanksand led to the dryer. The impressing roller is arranged to bear againstthe pellicle in a position where enough of the water will have beenremoved from the pellicle to insure the pellicle retaining the markafter complete drying.

The die used to impress the pellicle is preferably made of elasticvulcanized rubber, since this material is durable, conforms by reason ofits resilience to the contacted surface, and has less tendency to injurethe sheet than other materials. Other materials than rubber can be usedhowever, for example, wood, metal and artificial resins. These lattermaterials, however, since they are non-resilient, have a tendency topuncture or rupture the pellicle. When the impression isappliedmanually, the tendency of dies made of non-resilient material to rupturethe pellicle can be regulated to a great degree by a careful operation.However, when the impressing is done by machine, for example, by meansof a die roller, means should be used to overcome the rupturing tendencyof non-resilient .dies. Such means comp-rises suitably mounting theroller so as to permit it to ride freely on the pellicle, the pressurein this instance being imparted by the weight of the roller, or by usingspring mountings, counterweights, or similar mechanisms to accomplishthe same results. 7

It is evident from the above description that my invention comprises ahighly satisfactory method for permanently watermarking transparent,non-fibrous, non-porous, cellulosic pellicles. The term watermark, as ithas been used in describing this invention, is intended to signify atransparent mark resembling the watermark imparted to paper, which ispermanently imparted to the cellulosic pellicle, is visible bytransmitted light and which results from a treatment of the pellicleduring manufacture.

An advantage of this invention resides in its simplicity, greateificiency and inexpensiveness.

A further advantage of the invention resides in the fact that thewatermarks imparted to the to be understood that I do not limit myselfto' the specific embodiments thereof except as defined in the appendedclaims.

I claim:

1. An article of manufacture comprising a pellicle of regeneratedcellulose bearing a watermark, said watermark having been imparted tothe sheet by impressing the pellicle during the drying thereof and whilethe pellicle stillretained from 45 to moisture based on the weight ofthe dry pellicle plus softener.

2. The method of manufacturing a marked pellicle of regeneratedcellulose, which comprises casting, coagulating and regenerating thepollicle, partially drying the same, impressing the pellicle with a .diewhile the pellicle has a moisture content of between 45% and 190%, basedon the weight of the dry pellicle plus softener, and completing thedrying.

3. In the method of manufacturing watermarked pellicles of regeneratedcellulose which comprises casting, coagulating, regenerating, softeningand drying at pellicle, the step which comprises die-pressing thepellicle while its moisture content is 45% to 190% based on the weightof the dry pellicle plus softener.

4. A method of imparting a watermarkon a non-fibrous, transparentcellulosic pellicle comprising die-pressing the pellicle while itsmoisture content is 45-l90%, based on the weight of the dry pellicle,plus the softener.

5. A method of imparting a watermark on a regenerated cellulose pelliclecomprising diepressing the pellicle while its moisture content is45-l90%, based on the weight of the dry pellicle, plus the softener.

JAMES E. SNYDER.

